Aggressive data deduplication using lazy garbage collection

ABSTRACT

A method for extending data lifetime for reference in deduplication is provided. The method includes determining that a quantity of user data has at least a threshold amount of data that is re-created in a storage system. The method includes protecting at least portions of the quantity of user data from erasure by garbage collection in the storage system during a predetermined time interval, wherein the protected at least portions are available for data deduplication of further user data in the storage system during the predetermined time interval.

BACKGROUND

Solid-state memory, such as flash, is currently in use in solid-statedrives (SSD) to augment or replace conventional hard disk drives (HDD),writable CD (compact disk) or writable DVD (digital versatile disk)drives, collectively known as spinning media, and tape drives, forstorage of large amounts of data. Flash and other solid-state memorieshave characteristics that differ from spinning media. Yet, manysolid-state drives are designed to conform to hard disk drive standardsfor compatibility reasons, which makes it difficult to provide enhancedfeatures or take advantage of unique aspects of flash and othersolid-state memory. Solid-state storage memory, particularly flashmemory, may have limited write and erase cycle endurance, which poseobstacles in the use of solid-state storage memory for backup systemsand/or deduplication systems. In addition, some systems or applicationscreate the same or similar files over and over, for example forregression testing, unit testing, or during a synthesis and buildprocess. These systems and applications may also have ineffective datadeduplication.

It is within this context that the embodiments arise.

SUMMARY

In some embodiments a method for extending data lifetime for referencein deduplication is provided. The method includes determining that aquantity of user data has at least a threshold amount of data that isre-created in a storage system. The method includes protecting at leastportions of the quantity of user data from erasure by garbage collectionin the storage system during a predetermined time interval, wherein theprotected at least portions are available for data deduplication offurther user data in the storage system during the predetermined timeinterval.

In some embodiments, a deduplication method is provided. The methodincludes identifying user data having at least a threshold amount ofdata that is re-created, by one or more applications and writing anindicator to metadata associated with the identified user data, whereinthe indicator establishes a time interval of erasure immunity. Themethod includes preventing at least portions of the user data from beingerased during garbage collection, during the time interval in accordancewith the indicator in metadata, wherein the at least portions of theidentified user data are kept available during the time interval oferasure immunity as reference data for deduplication of further data.Erasure immunity refers to protecting files or blocks from erasure ordeletion during garbage collection processes. That is, the files orblocks having erasure immunity are not erased or deleted as thedesignated files or blocks are protected through a flag setting, or someother suitable mechanism, from deletion during the garbage collectionprocess. In some embodiments the method is embodied as instructionsstored on a computer readable medium.

In some embodiments, a storage system, with deduplication is provided.The system includes storage memory and at least one processor of thestorage system, configured to write an indicator to metadata of thestorage system. The indicator protects at least portions of user datafrom erasure during garbage collection, for a time interval, responsiveto the at least one processor identifying the user data as having atleast a threshold amount of data that is re-created on a periodic basis,wherein the at least portions of the user data associated with theindicator are available during the time interval as reference fordeduplication.

Other aspects and advantages of the embodiments will become apparentfrom the following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments and the advantages thereof may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings. These drawings in no waylimit any changes in form and detail that may be made to the describedembodiments by one skilled in the art without departing from the spiritand scope of the described embodiments.

FIG. 1 is a perspective view of a storage cluster with multiple storagenodes and internal storage coupled to each storage node to providenetwork attached storage, in accordance with some embodiments.

FIG. 2 is a block diagram showing an interconnect switch couplingmultiple storage nodes in accordance with some embodiments.

FIG. 3 is a multiple level block diagram, showing contents of a storagenode and contents of one of the non-volatile solid state storage unitsin accordance with some embodiments.

FIG. 4 is a storage system action diagram depicting deduplication ofdata from files, and garbage collection with specific data protected byerasure immunity, in accordance with some embodiments.

FIG. 5 depicts a histogram or other data structure that shows repeateddata in files and is suitable for identifying specific data to beprotected during garbage collection, per the operation shown in FIG. 4in accordance with some embodiments.

FIG. 6 depicts a metadata table that indicates erasure immunity forspecified files and is suitable for identifying specific data to beprotected during garbage collection, per the operation shown in FIG. 4in accordance with some embodiments.

FIG. 7 is a flow diagram of a method for extending data lifetime forreference in deduplication, which can be practiced using embodiments ofstorage nodes, storage units and storage clusters as shown in FIGS. 1-3,and embodiments of the system of FIGS. 4-6 in accordance with someembodiments.

FIG. 8 is an illustration showing an exemplary computing device whichmay implement the embodiments described herein.

DETAILED DESCRIPTION

The embodiments below describe a storage cluster that stores user data,such as data originating from one or more users or client systems orother sources external to the storage cluster. Some embodiments of thestorage clusters and storage systems are suitable for improvements todeduplication and garbage collection, as described further below. Thestorage cluster distributes user data across storage nodes housed withina chassis, using erasure coding and redundant copies of metadata.Erasure coding refers to a method of data protection or reconstructionin which data is stored across a set of different locations, such asdisks, storage nodes or geographic locations. Flash memory is one typeof solid-state memory that may be integrated with the embodiments,although the embodiments may be extended to other types of solid-statememory or other storage medium, including non-solid state memory.Control of storage locations and workloads are distributed across thestorage locations in a clustered peer-to-peer system. Tasks such asmediating communications between the various storage nodes, detectingwhen a storage node has become unavailable, and balancing I/Os (inputsand outputs) across the various storage nodes, are all handled on adistributed basis. Data is laid out or distributed across multiplestorage nodes in data fragments or stripes that support data recovery insome embodiments. Ownership of data can be reassigned within a cluster,independent of input and output patterns. This architecture described inmore detail below allows a storage node in the cluster to fail, with thesystem remaining operational, since the data can be reconstructed fromother storage nodes and thus remain available for input and outputoperations. In various embodiments, a storage node may be referred to asa cluster node, a blade, or a server.

The storage cluster is contained within a chassis, i.e., an enclosurehousing one or more storage nodes. A mechanism to provide power to eachstorage node, such as a power distribution bus, and a communicationmechanism, such as a communication bus that enables communicationbetween the storage nodes are included within the chassis. The storagecluster can run as an independent system in one location according tosome embodiments. In one embodiment, a chassis contains at least twoinstances of both the power distribution and the communication bus whichmay be enabled or disabled independently. The internal communication busmay be an Ethernet bus, however, other technologies such as PeripheralComponent Interconnect (PCI) Express, InfiniBand, and others, areequally suitable. The chassis provides a port for an externalcommunication bus for enabling communication between multiple chassis,directly or through a switch, and with client systems. The externalcommunication may use a technology such as Ethernet, InfiniBand, FibreChannel, etc. In some embodiments, the external communication bus usesdifferent communication bus technologies for inter-chassis and clientcommunication. If a switch is deployed within or between chassis, theswitch may act as a translation between multiple protocols ortechnologies. When multiple chassis are connected to define a storagecluster, the storage cluster may be accessed by a client using eitherproprietary interfaces or standard interfaces such as network filesystem (NFS), common internet file system (CIFS), small computer systeminterface (SCSI) or hypertext transfer protocol (HTTP). Translation fromthe client protocol may occur at the switch, chassis externalcommunication bus or within each storage node.

Each storage node may be one or more storage servers and each storageserver is connected to one or more non-volatile solid state memoryunits, which may be referred to as storage units. One embodimentincludes a single storage server in each storage node and between one toeight non-volatile solid state memory units, however this one example isnot meant to be limiting. The storage server may include a processor,dynamic random access memory (DRAM) and interfaces for the internalcommunication bus and power distribution for each of the power buses.Inside the storage node, the interfaces and storage unit share acommunication bus, e.g., PCI Express, in some embodiments. Thenon-volatile solid state memory units may directly access the internalcommunication bus interface through a storage node communication bus, orrequest the storage node to access the bus interface. The non-volatilesolid state memory unit contains an embedded central processing unit(CPU), solid state storage controller, and a quantity of solid statemass storage, e.g., between 2-32 terabytes (TB) in some embodiments. Anembedded volatile storage medium, such as DRAM, and an energy reserveapparatus are included in the non-volatile solid state memory unit. Insome embodiments, the energy reserve apparatus is a capacitor,super-capacitor, or battery that enables transferring a subset of DRAMcontents to a stable storage medium in the case of power loss. In someembodiments, the non-volatile solid state memory unit is constructedwith a storage class memory, such as phase change or magnetoresistiverandom access memory (MRAM) that substitutes for DRAM and enables areduced power hold-up apparatus.

One of many features of the storage nodes and non-volatile solid statestorage is the ability to proactively rebuild data in a storage cluster.The storage nodes and non-volatile solid state storage can determinewhen a storage node or non-volatile solid state storage in the storagecluster is unreachable, independent of whether there is an attempt toread data involving that storage node or non-volatile solid statestorage. The storage nodes and non-volatile solid state storage thencooperate to recover and rebuild the data in at least partially newlocations. This constitutes a proactive rebuild, in that the systemrebuilds data without waiting until the data is needed for a read accessinitiated from a client system employing the storage cluster. These andfurther details of the storage memory and operation thereof arediscussed below.

FIG. 1 is a perspective view of a storage cluster 160, with multiplestorage nodes 150 and internal solid-state memory coupled to eachstorage node to provide network attached storage or storage areanetwork, in accordance with some embodiments. A network attachedstorage, storage area network, or a storage cluster, or other storagememory, could include one or more storage clusters 160, each having oneor more storage nodes 150, in a flexible and reconfigurable arrangementof both the physical components and the amount of storage memoryprovided thereby. The storage cluster 160 is designed to fit in a rack,and one or more racks can be set up and populated as desired for thestorage memory. The storage cluster 160 has a chassis 138 havingmultiple slots 142. It should be appreciated that chassis 138 may bereferred to as a housing, enclosure, or rack unit. In one embodiment,the chassis 138 has fourteen slots 142, although other numbers of slotsare readily devised. For example, some embodiments have four slots,eight slots, sixteen slots, thirty-two slots, or other suitable numberof slots. Each slot 142 can accommodate one storage node 150 in someembodiments. Chassis 138 includes flaps 148 that can be utilized tomount the chassis 138 on a rack. Fans 144 provide air circulation forcooling of the storage nodes 150 and components thereof, although othercooling components could be used, or an embodiment could be devisedwithout cooling components. A switch fabric 146 couples storage nodes150 within chassis 138 together and to a network for communication tothe memory. In an embodiment depicted in FIG. 1, the slots 142 to theleft of the switch fabric 146 and fans 144 are shown occupied by storagenodes 150, while the slots 142 to the right of the switch fabric 146 andfans 144 are empty and available for insertion of storage node 150 forillustrative purposes. This configuration is one example, and one ormore storage nodes 150 could occupy the slots 142 in various furtherarrangements. The storage node arrangements need not be sequential oradjacent in some embodiments. Storage nodes 150 are hot pluggable,meaning that a storage node 150 can be inserted into a slot 142 in thechassis 138, or removed from a slot 142, without stopping or poweringdown the system. Upon insertion or removal of storage node 150 from slot142, the system automatically reconfigures in order to recognize andadapt to the change. Reconfiguration, in some embodiments, includesrestoring redundancy and/or rebalancing data or load.

Each storage node 150 can have multiple components. In the embodimentshown here, the storage node 150 includes a printed circuit board 158populated by a CPU 156, i.e., processor, a memory 154 coupled to the CPU156, and a non-volatile solid state storage 152 coupled to the CPU 156,although other mountings and/or components could be used in furtherembodiments. The memory 154 has instructions which are executed by theCPU 156 and/or data operated on by the CPU 156. As further explainedbelow, the non-volatile solid state storage 152 includes flash or, infurther embodiments, other types of solid-state memory.

Referring to FIG. 1, storage cluster 160 is scalable, meaning thatstorage capacity with non-uniform storage sizes is readily added, asdescribed above. One or more storage nodes 150 can be plugged into orremoved from each chassis and the storage cluster self-configures insome embodiments. Plug-in storage nodes 150, whether installed in achassis as delivered or later added, can have different sizes. Forexample, in one embodiment a storage node 150 can have any multiple of 4TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, astorage node 150 could have any multiple of other storage amounts orcapacities. Storage capacity of each storage node 150 is broadcast, andinfluences decisions of how to stripe the data. For maximum storageefficiency, an embodiment can self-configure as wide as possible in thestripe, subject to a predetermined requirement of continued operationwith loss of up to one, or up to two, non-volatile solid state storageunits 152 or storage nodes 150 within the chassis.

FIG. 2 is a block diagram showing a communications interconnect 170 andpower distribution bus 172 coupling multiple storage nodes 150.Referring back to FIG. 1, the communications interconnect 170 can beincluded in or implemented with the switch fabric 146 in someembodiments. Where multiple storage clusters 160 occupy a rack, thecommunications interconnect 170 can be included in or implemented with atop of rack switch, in some embodiments. As illustrated in FIG. 2,storage cluster 160 is enclosed within a single chassis 138. Externalport 176 is coupled to storage nodes 150 through communicationsinterconnect 170, while external port 174 is coupled directly to astorage node. External power port 178 is coupled to power distributionbus 172. Storage nodes 150 may include varying amounts and differingcapacities of non-volatile solid state storage 152 as described withreference to FIG. 1. In addition, one or more storage nodes 150 may be acompute only storage node as illustrated in FIG. 2. Authorities 168 areimplemented on the non-volatile solid state storages 152, for example aslists or other data structures stored in memory. In some embodiments theauthorities are stored within the non-volatile solid state storage 152and supported by software executing on a controller or other processorof the non-volatile solid state storage 152. In a further embodiment,authorities 168 are implemented on the storage nodes 150, for example aslists or other data structures stored in the memory 154 and supported bysoftware executing on the CPU 156 of the storage node 150. Authorities168 control how and where data is stored in the non-volatile solid statestorages 152 in some embodiments. This control assists in determiningwhich type of erasure coding scheme is applied to the data, and whichstorage nodes 150 have which portions of the data. Each authority 168may be assigned to a non-volatile solid state storage 152. Eachauthority may control a range of inode numbers, segment numbers, orother data identifiers which are assigned to data by a file system, bythe storage nodes 150, or by the non-volatile solid state storage 152,in various embodiments.

Every piece of data, and every piece of metadata, has redundancy in thesystem in some embodiments. In addition, every piece of data and everypiece of metadata has an owner, which may be referred to as anauthority. If that authority is unreachable, for example through failureof a storage node, there is a plan of succession for how to find thatdata or that metadata. In various embodiments, there are redundantcopies of authorities 168. Authorities 168 have a relationship tostorage nodes 150 and non-volatile solid state storage 152 in someembodiments. Each authority 168, covering a range of data segmentnumbers or other identifiers of the data, may be assigned to a specificnon-volatile solid state storage 152. In some embodiments theauthorities 168 for all of such ranges are distributed over thenon-volatile solid state storages 152 of a storage cluster. Each storagenode 150 has a network port that provides access to the non-volatilesolid state storage(s) 152 of that storage node 150. Data can be storedin a segment, which is associated with a segment number and that segmentnumber is an indirection for a configuration of a RAID (redundant arrayof independent disks) stripe in some embodiments. The assignment and useof the authorities 168 thus establishes an indirection to data.Indirection may be referred to as the ability to refer to dataindirectly, in this case via an authority 168, in accordance with someembodiments. A segment identifies a set of non-volatile solid statestorage 152 and a local identifier into the set of non-volatile solidstate storage 152 that may contain data. In some embodiments, the localidentifier is an offset into the device and may be reused sequentiallyby multiple segments. In other embodiments the local identifier isunique for a specific segment and never reused. The offsets in thenon-volatile solid state storage 152 are applied to locating data forwriting to or reading from the non-volatile solid state storage 152 (inthe form of a RAID stripe). Data is striped across multiple units ofnon-volatile solid state storage 152, which may include or be differentfrom the non-volatile solid state storage 152 having the authority 168for a particular data segment.

If there is a change in where a particular segment of data is located,e.g., during a data move or a data reconstruction, the authority 168 forthat data segment should be consulted, at that non-volatile solid statestorage 152 or storage node 150 having that authority 168. In order tolocate a particular piece of data, embodiments calculate a hash valuefor a data segment or apply an inode number or a data segment number.The output of this operation points to a non-volatile solid statestorage 152 having the authority 168 for that particular piece of data.In some embodiments there are two stages to this operation. The firststage maps an entity identifier (ID), e.g., a segment number, inodenumber, or directory number to an authority identifier. This mapping mayinclude a calculation such as a hash or a bit mask. The second stage ismapping the authority identifier to a particular non-volatile solidstate storage 152, which may be done through an explicit mapping. Theoperation is repeatable, so that when the calculation is performed, theresult of the calculation repeatably and reliably points to a particularnon-volatile solid state storage 152 having that authority 168. Theoperation may include the set of reachable storage nodes as input. Ifthe set of reachable non-volatile solid state storage units changes theoptimal set changes. In some embodiments, the persisted value is thecurrent assignment (which is always true) and the calculated value isthe target assignment the cluster will attempt to reconfigure towards.This calculation may be used to determine the optimal non-volatile solidstate storage 152 for an authority in the presence of a set ofnon-volatile solid state storage 152 that are reachable and constitutethe same cluster. The calculation also determines an ordered set of peernon-volatile solid state storage 152 that will also record the authorityto non-volatile solid state storage mapping so that the authority may bedetermined even if the assigned non-volatile solid state storage isunreachable. A duplicate or substitute authority 168 may be consulted ifa specific authority 168 is unavailable in some embodiments.

With reference to FIGS. 1 and 2, two of the many tasks of the CPU 156 ona storage node 150 are to break up write data, and reassemble read data.When the system has determined that data is to be written, the authority168 for that data is located as above. When the segment ID for data isalready determined the request to write is forwarded to the non-volatilesolid state storage 152 currently determined to be the host of theauthority 168 determined from the segment. The host CPU 156 of thestorage node 150, on which the non-volatile solid state storage 152 andcorresponding authority 168 reside, then breaks up or shards the dataand transmits the data out to various non-volatile solid state storage152. The transmitted data is written as a data stripe in accordance withan erasure coding scheme. In some embodiments, data is requested to bepulled, and in other embodiments, data is pushed. In reverse, when datais read, the authority 168 for the segment ID containing the data islocated as described above. The host CPU 156 of the storage node 150 onwhich the non-volatile solid state storage 152 and correspondingauthority 168 reside requests the data from the non-volatile solid statestorage and corresponding storage nodes pointed to by the authority. Insome embodiments the data is read from flash storage as a data stripe.The host CPU 156 of storage node 150 then reassembles the read data,correcting any errors (if present) according to the appropriate erasurecoding scheme, and forwards the reassembled data to the network. Infurther embodiments, some or all of these tasks can be handled in thenon-volatile solid state storage 152. In some embodiments, the segmenthost requests the data be sent to storage node 150 by requesting pagesfrom storage and then sending the data to the storage node making theoriginal request.

In some systems, for example in UNIX-style file systems, data is handledwith an index node or inode, which specifies a data structure thatrepresents an object in a file system. The object could be a file or adirectory, for example. Metadata may accompany the object, as attributessuch as permission data and a creation timestamp, among otherattributes. A segment number could be assigned to all or a portion ofsuch an object in a file system. In other systems, data segments arehandled with a segment number assigned elsewhere. For purposes ofdiscussion, the unit of distribution is an entity, and an entity can bea file, a directory or a segment. That is, entities are units of data ormetadata stored by a storage system. Entities are grouped into setscalled authorities. Each authority has an authority owner, which is astorage node that has the exclusive right to update the entities in theauthority. In other words, a storage node contains the authority, andthat the authority, in turn, contains entities.

A segment is a logical container of data in accordance with someembodiments. A segment is an address space between medium address spaceand physical flash locations, i.e., the data segment number, are in thisaddress space. Segments may also contain meta-data, which enable dataredundancy to be restored (rewritten to different flash locations ordevices) without the involvement of higher level software. In oneembodiment, an internal format of a segment contains client data andmedium mappings to determine the position of that data. Each datasegment is protected, e.g., from memory and other failures, by breakingthe segment into a number of data and parity shards, where applicable.The data and parity shards are distributed, i.e., striped, acrossnon-volatile solid state storage 152 coupled to the host CPUs 156 (SeeFIG. 5) in accordance with an erasure coding scheme. Usage of the termsegments refers to the container and its place in the address space ofsegments in some embodiments. Usage of the term stripe refers to thesame set of shards as a segment and includes how the shards aredistributed along with redundancy or parity information in accordancewith some embodiments.

A series of address-space transformations takes place across an entirestorage system. At the top are the directory entries (file names) whichlink to an inode. Inodes point into medium address space, where data islogically stored. Medium addresses may be mapped through a series ofindirect mediums to spread the load of large files, or implement dataservices like deduplication or snapshots. Medium addresses may be mappedthrough a series of indirect mediums to spread the load of large files,or implement data services like deduplication or snapshots. Segmentaddresses are then translated into physical flash locations. Physicalflash locations have an address range bounded by the amount of flash inthe system in accordance with some embodiments. Medium addresses andsegment addresses are logical containers, and in some embodiments use a128 bit or larger identifier so as to be practically infinite, with alikelihood of reuse calculated as longer than the expected life of thesystem. Addresses from logical containers are allocated in ahierarchical fashion in some embodiments. Initially, each non-volatilesolid state storage 152 may be assigned a range of address space. Withinthis assigned range, the non-volatile solid state storage 152 is able toallocate addresses without synchronization with other non-volatile solidstate storage 152.

Data and metadata is stored by a set of underlying storage layouts thatare optimized for varying workload patterns and storage devices. Theselayouts incorporate multiple redundancy schemes, compression formats andindex algorithms. Some of these layouts store information aboutauthorities and authority masters, while others store file metadata andfile data. The redundancy schemes include error correction codes thattolerate corrupted bits within a single storage device (such as a NANDflash chip), erasure codes that tolerate the failure of multiple storagenodes, and replication schemes that tolerate data center or regionalfailures. In some embodiments, low density parity check (LDPC) code isused within a single storage unit. Reed-Solomon encoding is used withina storage cluster, and mirroring is used within a storage grid in someembodiments. Metadata may be stored using an ordered log structuredindex (such as a Log Structured Merge Tree), and large data may not bestored in a log structured layout.

In order to maintain consistency across multiple copies of an entity,the storage nodes agree implicitly on two things through calculations:(1) the authority that contains the entity, and (2) the storage nodethat contains the authority. The assignment of entities to authoritiescan be done by pseudorandomly assigning entities to authorities, bysplitting entities into ranges based upon an externally produced key, orby placing a single entity into each authority. Examples of pseudorandomschemes are linear hashing and the Replication Under Scalable Hashing(RUSH) family of hashes, including Controlled Replication Under ScalableHashing (CRUSH). In some embodiments, pseudo-random assignment isutilized only for assigning authorities to nodes because the set ofnodes can change. The set of authorities cannot change so any subjectivefunction may be applied in these embodiments. Some placement schemesautomatically place authorities on storage nodes, while other placementschemes rely on an explicit mapping of authorities to storage nodes. Insome embodiments, a pseudorandom scheme is utilized to map from eachauthority to a set of candidate authority owners. A pseudorandom datadistribution function related to CRUSH may assign authorities to storagenodes and create a list of where the authorities are assigned. Eachstorage node has a copy of the pseudorandom data distribution function,and can arrive at the same calculation for distributing, and laterfinding or locating an authority. Each of the pseudorandom schemesrequires the reachable set of storage nodes as input in some embodimentsin order to conclude the same target nodes. Once an entity has beenplaced in an authority, the entity may be stored on physical devices sothat no expected failure will lead to unexpected data loss. In someembodiments, rebalancing algorithms attempt to store the copies of allentities within an authority in the same layout and on the same set ofmachines.

Examples of expected failures include device failures, stolen machines,datacenter fires, and regional disasters, such as nuclear or geologicalevents. Different failures lead to different levels of acceptable dataloss. In some embodiments, a stolen storage node impacts neither thesecurity nor the reliability of the system, while depending on systemconfiguration, a regional event could lead to no loss of data, a fewseconds or minutes of lost updates, or even complete data loss.

In the embodiments, the placement of data for storage redundancy isindependent of the placement of authorities for data consistency. Insome embodiments, storage nodes that contain authorities do not containany persistent storage. Instead, the storage nodes are connected tonon-volatile solid state storage units that do not contain authorities.The communications interconnect between storage nodes and non-volatilesolid state storage units consists of multiple communicationtechnologies and has non-uniform performance and fault tolerancecharacteristics. In some embodiments, as mentioned above, non-volatilesolid state storage units are connected to storage nodes via PCIexpress, storage nodes are connected together within a single chassisusing Ethernet backplane, and chassis are connected together to form astorage cluster. Storage clusters are connected to clients usingEthernet or fiber channel in some embodiments. If multiple storageclusters are configured into a storage grid, the multiple storageclusters are connected using the Internet or other long-distancenetworking links, such as a “metro scale” link or private link that doesnot traverse the internet.

Authority owners have the exclusive right to modify entities, to migrateentities from one non-volatile solid state storage unit to anothernon-volatile solid state storage unit, and to add and remove copies ofentities. This allows for maintaining the redundancy of the underlyingdata. When an authority owner fails, is going to be decommissioned, oris overloaded, the authority is transferred to a new storage node.Transient failures make it non-trivial to ensure that all non-faultymachines agree upon the new authority location. The ambiguity thatarises due to transient failures can be achieved automatically by aconsensus protocol such as Paxos, hot-warm failover schemes, via manualintervention by a remote system administrator, or by a local hardwareadministrator (such as by physically removing the failed machine fromthe cluster, or pressing a button on the failed machine). In someembodiments, a consensus protocol is used, and failover is automatic. Iftoo many failures or replication events occur in too short a timeperiod, the system goes into a self-preservation mode and haltsreplication and data movement activities until an administratorintervenes in accordance with some embodiments.

As authorities are transferred between storage nodes and authorityowners update entities in their authorities, the system transfersmessages between the storage nodes and non-volatile solid state storageunits. With regard to persistent messages, messages that have differentpurposes are of different types. Depending on the type of the message,the system maintains different ordering and durability guarantees. Asthe persistent messages are being processed, the messages aretemporarily stored in multiple durable and non-durable storage hardwaretechnologies. In some embodiments, messages are stored in RAM, NVRAM andon NAND flash devices, and a variety of protocols are used in order tomake efficient use of each storage medium. Latency-sensitive clientrequests may be persisted in replicated NVRAM, and then later NAND,while background rebalancing operations are persisted directly to NAND.

Persistent messages are persistently stored prior to being replicated.This allows the system to continue to serve client requests despitefailures and component replacement. Although many hardware componentscontain unique identifiers that are visible to system administrators,manufacturer, hardware supply chain and ongoing monitoring qualitycontrol infrastructure, applications running on top of theinfrastructure address virtualize addresses. These virtualized addressesdo not change over the lifetime of the storage system, regardless ofcomponent failures and replacements. This allows each component of thestorage system to be replaced over time without reconfiguration ordisruptions of client request processing.

In some embodiments, the virtualized addresses are stored withsufficient redundancy. A continuous monitoring system correlateshardware and software status and the hardware identifiers. This allowsdetection and prediction of failures due to faulty components andmanufacturing details. The monitoring system also enables the proactivetransfer of authorities and entities away from impacted devices beforefailure occurs by removing the component from the critical path in someembodiments.

FIG. 3 is a multiple level block diagram, showing contents of a storagenode 150 and contents of a non-volatile solid state storage 152 of thestorage node 150. Data is communicated to and from the storage node 150by a network interface controller (NIC) 202 in some embodiments. Eachstorage node 150 has a CPU 156, and one or more non-volatile solid statestorage 152, as discussed above. Moving down one level in FIG. 3, eachnon-volatile solid state storage 152 has a relatively fast non-volatilesolid state memory, such as nonvolatile random access memory (NVRAM)204, and flash memory 206. In some embodiments, NVRAM 204 may be acomponent that does not require program/erase cycles (DRAM, MRAM, PCM),and can be a memory that can support being written vastly more oftenthan the memory is read from. Moving down another level in FIG. 3, theNVRAM 204 is implemented in one embodiment as high speed volatilememory, such as dynamic random access memory (DRAM) 216, backed up byenergy reserve 218. Energy reserve 218 provides sufficient electricalpower to keep the DRAM 216 powered long enough for contents to betransferred to the flash memory 206 in the event of power failure. Insome embodiments, energy reserve 218 is a capacitor, super-capacitor,battery, or other device, that supplies a suitable supply of energysufficient to enable the transfer of the contents of DRAM 216 to astable storage medium in the case of power loss. The flash memory 206 isimplemented as multiple flash dies 222, which may be referred to aspackages of flash dies 222 or an array of flash dies 222. It should beappreciated that the flash dies 222 could be packaged in any number ofways, with a single die per package, multiple dies per package (i.e.multichip packages), in hybrid packages, as bare dies on a printedcircuit board or other substrate, as encapsulated dies, etc. In theembodiment shown, the non-volatile solid state storage 152 has acontroller 212 or other processor, and an input output (I/O) port 210coupled to the controller 212. I/O port 210 is coupled to the CPU 156and/or the network interface controller 202 of the flash storage node150. Flash input output (I/O) port 220 is coupled to the flash dies 222,and a direct memory access unit (DMA) 214 is coupled to the controller212, the DRAM 216 and the flash dies 222. In the embodiment shown, theI/O port 210, controller 212, DMA unit 214 and flash I/O port 220 areimplemented on a programmable logic device (PLD) 208, e.g., a fieldprogrammable gate array (FPGA). In this embodiment, each flash die 222has pages, organized as sixteen kB (kilobyte) pages 224, and a register226 through which data can be written to or read from the flash die 222.In further embodiments, other types of solid-state memory are used inplace of, or in addition to flash memory illustrated within flash die222.

Storage clusters 160, in various embodiments as disclosed herein, can becontrasted with storage arrays in general. The storage nodes 150 arepart of a collection that creates the storage cluster 160. Each storagenode 150 owns a slice of data and computing required to provide thedata. Multiple storage nodes 150 cooperate to store and retrieve thedata. Storage memory or storage devices, as used in storage arrays ingeneral, are less involved with processing and manipulating the data.Storage memory or storage devices in a storage array receive commands toread, write, or erase data. The storage memory or storage devices in astorage array are not aware of a larger system in which they areembedded, or what the data means. Storage memory or storage devices instorage arrays can include various types of storage memory, such as RAM,solid state drives, hard disk drives, etc. The storage units 152described herein have multiple interfaces active simultaneously andserving multiple purposes. In some embodiments, some of thefunctionality of a storage node 150 is shifted into a storage unit 152,transforming the storage unit 152 into a combination of storage unit 152and storage node 150. Placing computing (relative to storage data) intothe storage unit 152 places this computing closer to the data itself.The various system embodiments have a hierarchy of storage node layerswith different capabilities. By contrast, in a storage array, acontroller owns and knows everything about all of the data that thecontroller manages in a shelf or storage devices. In a storage cluster160, as described herein, multiple controllers in multiple storage units152 and/or storage nodes 150 cooperate in various ways (e.g., forerasure coding, data sharding, metadata communication and redundancy,storage capacity expansion or contraction, data recovery, and so on).

FIG. 4 is a storage system action diagram depicting deduplication 414 ofdata from files 410, and garbage collection 422 with specific dataprotected by erasure immunity, in an embodiment of the presentdisclosure. As mentioned above, erasure immunity refers to protectingfiles or blocks from erasure or deletion during garbage collectionprocesses. That is, the files or blocks having erasure immunity are noterased or deleted as the designated files or blocks are protectedthrough a flag setting, or some other suitable mechanism, from deletionduring the garbage collection process. Deduplication 414 reduces oreliminates redundant or duplicate data, and can be practiced inline(also known as on-the-fly) or post-process. Examples of inlinededuplication include deduplication during data creation and datainjection (e.g., to a storage system), and deduplication during a backuprun. Examples of post-process deduplication include deduplication afterdata creation or data injection, and deduplication after a backup run.Both types of deduplication may be integrated into the mechanismsdescribed herein. A brief overview of deduplication 414 is given below,followed by description of improvements to deduplication 414 inaccordance with present embodiments. It should be appreciated that otherdeduplication scenarios may benefit from the improvements describedherein. In one scenario, one or more applications 408, operating under afile system 402, create files 410. The files 410 are sent fordeduplication 414. Deduplication 414 could be inline deduplication ofthe files 410 as they are created, or as they are sent for storage in astorage cluster 160. In some embodiments the files 410 could be storedin a storage cluster 160, and then subjected to post-processdeduplication. The deduplication 414 process typically performs a hashfunction 416 on each data portion 412, and forms a fingerprint of thedata portion 412. The fingerprint is checked against fingerprints 418 of(i.e., that reference) various data portions in a storage 420. If thefingerprint of the data portion 412 matches one of the fingerprints 418,the data portion 412 is discarded (shown symbolically with an arrowpointing towards a trashcan 432). If no match is found for thefingerprint of the data portion 412, the data portion 412 is sent to thestorage 420. Various algorithms for maintenance of fingerprints 418, anddecisions on how, or how deep, to search for fingerprint matches, arecommonly available and can be integrated with the embodiments described.It should be appreciated that data portion 412 may be a file based dataportion, object based date portion, or a block based data portion.

A deduplication 414 process references data through multiple techniquesor instances. One instance is during the comparison process, in whichthe deduplication 414 references data using the fingerprints 418 toidentify a match to a fingerprint of a data portion 412 underconsideration for storage or discarding. A second instance adeduplication 414 process references data is in storage of file links. Adeduplicated file is represented as a set of references to data portionsand stored as a series of links to data portions. These links canreference unique data portions 412 in the storage 420, or data portions412 that have multiple references as a result of matching data portions412 that were discarded. A third instance a deduplication 414 processreferences data is when a file is reconstructed from the series oflinks, and the deduplication 414 process locates the referenced dataportions 412 and reassembles a file, e.g., in a file restoration processfrom a backup image. In some embodiments, reference data as used hereinmay refer to any of the data, i.e., fingerprints, file links,reassembled files, objects, etc., used in the deduplication techniquesor instances mentioned in this paragraph.

Continuing with the scenario of FIG. 4, an application 408 uses the filecreate 404 process of the file system 402 in order to create a file 410,and uses the file delete 406 process of the file system 402 in order todelete a file 410. In a storage system, such as the storage cluster 160described with reference to FIGS. 1-3, a garbage collection 422 processidentifies memory locations in the storage 420, for which the filesystem 402 says the data no longer exists. For flash memory, the garbagecollection 422 would erase blocks of flash, under such circumstances(except as described below, per erasure immunity). In other words, if afile has been deleted, it is normally acceptable for the garbagecollection 422 process to erase corresponding flash memory blocks, orotherwise arrange for reuse of memory corresponding to the no longerexisting data. That is, since the file or block no longer exists andthere are no other references to that data by other files or blocks andthus it is a candidate for immediate garbage collection. The embodimentsexploit temporal locality of recreating that data to prevent garbagecollection from reclaiming the data blocks, reducing flash wear andextending the lifetime of the flash media. It should be appreciated thatthe particulars of garbage collection 422 are specific to anarchitecture, a storage memory type, and other system aspects. Inaddition, while the embodiments have provided examples referring tofiles and file systems, the embodiments may be extended to object orblock based systems also.

Garbage collection 422 can be problematic for deduplication 414, insystems where the same or similar files are created multiple times. Thiscan happen in systems built for regression testing, unit testing, orsynthesis and build processes. In these systems, files, objects, orblocks are created by certain applications 408 on a regular or irregularbasis and many such files, objects, or blocks have a large amount ofdata that is identical to data in previously seen files, objects, orblocks, i.e., the data is re-created. For example, temporary files,object files, simulation files and other files, objects, or blocksassociated with the above-described uses can be created on a weekly,daily, or even multiple times daily basis, and many of these files,objects, or blocks have data that is repeated from the previous run(s),i.e., re-created data. In some embodiments with respect to block basedsystems, logical block addresses may be repeatedly used in the system.If each of these runs is deduplicated, and garbage collection 422 isapplied, the same data gets erased, rewritten, erased and rewritten manytimes over the course of months or a year or some other time period.This situation is not only inefficient from a standpoint of systemactivity and time, but may result in rapid or premature wear of flashmemory or other storage memory types with wear limitations.

Still referring to FIG. 4, improvements to the garbage collection 422process include identifying and protecting specific data, by grantingerasure immunity for an erasure immunity time interval. The system isobserved (depicted symbolically as a funnel 430 collecting observationsabout the applications 408 and the file system 402) by a behavioranalysis module 424. The behavior analysis module 424 could beimplemented as software, firmware, hardware, or combinations thereof,for example on one or more storage nodes 150, or on one or morecompute-only nodes, in the storage cluster 160. The behavior analysismodule 424 produces a histogram 426 or other data structure, whichtracks file and data behavior as will be further described withreference to FIG. 5. File names or file types that are repeated, or thathave greater than a specified amount of repeated previously seen data,are detected by the behavior analysis module 424, for example throughanalysis of the histogram 426 or other data structure. The behavioranalysis module 424 then writes to a metadata table 428, as will befurther described with reference to FIG. 6. The metadata table 428indicates which files have erasure immunity and should be protectedduring garbage collection 422. Files with large amounts of re-createddata, i.e., new files in which data from previously seen files isrepeated in the new files, are candidates for erasure immunity duringgarbage collection 422. When garbage collection 422 is performed, fileswith erasure immunity are not erased, even if the file system 402indicates these files have been deleted and are no longer in existence.In variations, erasure immunity could be granted for blocks, or otheramounts of data. The files, blocks or other portions of data that aregranted erasure immunity are kept available during the erasure immunitytime interval as reference data for deduplication of further data.

FIG. 5 depicts a histogram 426 or other data structure that showsrepeated data in files 410 and is suitable for identifying specific datato be protected during garbage collection 422, per the operation shownin FIG. 4. Format for such a data structure is readily devised, and neednot be identical to the representation in FIG. 5. The application(s) 408are shown creating files 410 on a repeated basis, for purposes ofillustration of the contents of the histogram 426. In one embodiment,file names 502 are listed in the histogram 426. For each file name 502,a first indication 504 shows the amount of repeated (i.e., recurring,re-created) data in the file. That is, the contents of the file arecompared to previously seen files, and the amount of re-created orrepeated data in the file is noted in the histogram 426. This comparisoncould be made with use of the hash function 416, the fingerprints 418,or other comparison mechanism or utility. For each file name 502, asecond indication 506 illustrates the frequency of repetition of thefile. For example, the first entry in the histogram 426 shows a filewith a file name 502 “FILE01.TMP”. This file has about 50% repeated(i.e., re-created) data, and the file is created on a frequency ofrepetition of every few hours. Although shown in graphical format, thefirst and second indications 504, 506 could be in numerical format insome embodiments. Example file types that could have re-created datainclude temporary files (.TMP), object files (.OBJ) and simulation files(.SIM), among others. The value of the threshold, for the amount of datathat is re-created or repeated, could be adjusted based on the histogram426, or based on utilization ratios of storage memory, i.e., utilizationof storage capacity of the storage system.

FIG. 6 depicts a metadata table 428 that indicates erasure immunity 602for specified files and is suitable for identifying specific data to beprotected during garbage collection, per the operation shown in FIG. 4.For example, the behavior analysis module 424 could grant erasureimmunity 602, e.g., as shown with the entry “yes” in the metadata table428, to files having greater than 50% repeated data (or meeting someother threshold). In various embodiments, the metadata table 428 couldbe a separate table or could be integrated into a fingerprint table,e.g., with fingerprints 418 as shown in FIG. 4. In one embodiment,fingerprints 418 associated with a file that is granted erasure immunityalso have erasure immunity. An aging parameter 604 is established in themetadata table 428, in some embodiments. For example, the behavioranalysis module 424 could establish a lower aging parameter 604 forfiles found to have a rapid frequency of repetition (e.g., in hours ordays), and a higher aging parameter 604 for files found to have a lowerfrequency of repetition (e.g., in days or weeks) and thus in need of alonger extended lifetime or lifespan. The aging parameter 604 could bedecremented (i.e., counted down) at regular time spans (e.g., once perhour, once per day, or once per week) in some embodiments, or with eachgarbage collection 422 cycle, or with each deduplication 414 cycle, inother embodiments. In this manner, the combination of the erasureimmunity 602 and the aging parameter 604 establishes an extendedlifetime for specified files 410, according to the file names 502.Alternative parameters to an aging parameter may be incorporated intothe embodiments and these parameters may be combined with the agingparameter or utilized in place of the aging parameter. For example, aparameter such as a block size, object size or file size may be used asa tiebreaker to prioritize one block, object or file over another block,object or file where 2 blocks, objects or files have the same agingparameter. Thus, the embodiments are not limited to an aging parameteror a single parameter, as a combination of features that can includeage, size, etc., may be integrated with the embodiments to prioritize orfunction as a tie breaker in some embodiments. The extended lifetimegrants erasure immunity to a file during garbage collection 422,regardless of whether or not the file system 402 declares the file hasbeen deleted. The extended lifetime is valid until the lifetime expiresin some embodiments. In some embodiments, the extended lifetime can berenewed. For example, the behavior analysis module 424 could track filecreation and deletion patterns, allowing extended lifetimes to expireafter a specified number of dead cycles in which a file creation anddeletion pattern ceases, but renew appropriate extended lifetimes if thefile creation and deletion pattern resumes. The behavior analysis module424 could have awareness of calendars (e.g., weekends, holidays, plantshutdowns) and apply this in determining extended lifetimes orexpirations thereof. Thus, in various embodiments, depending uponsophistication of the algorithm, the time interval for erasure immunityof data could be a fixed time interval, or a variable one. In someembodiments, the erasure immunity time interval, whether fixed orvariable, is adjusted based on the amount of storage capacity utilized.For example, as storage capacity utilization increases, the erasureimmunity time interval could be decreased, so as not to overflow thestorage capacity. For situations in which there is a relatively lowstorage capacity utilization, a longer erasure immunity time intervalcould be used. In some embodiments related to write rates, if the writerate is very low, then garbage collection is less likely to beactivated, whereas relatively high write rates, even in low capacityresults in a garbage collection mechanism that is more active andrequires more management.

FIG. 7 is a flow diagram of a method for extending reference datalifetime in a deduplication mechanism, which can be practiced usingembodiments of storage nodes, storage units and storage clusters asshown in FIGS. 1-3, and embodiments of the system of FIGS. 4-6. Themethod can be practiced by one or more processors, such as processors ofstorage nodes, storage units or compute nodes. In a decision action 702,it is determined whether user data has greater than a threshold amountof re-created data. As noted above, the user data may be any data from aclient or source external to the storage system in some embodiments,which includes meta data. Re-created data refers to data that isrepeated in files as described above. If the user data does not havegreater than a threshold amount of re-created data, flow loops back tothe decision action 702 (or could branch elsewhere for furtherprocesses). If the user data does have greater than a threshold amountof re-created data, flow proceeds to the action 704. In the action 704,files, blocks or portions of data that include greater than a thresholdamount of re-created data are identified. These files, blocks orportions of data are granted erasure immunity, which is established inmetadata, in an action 706. Each of these erasure immune files, blocksor portions of data are granted an erasure immunity time interval, whichis also established in metadata, in an action 708. Regardless of whetherthe file system indicates a deleted file, a deleted block, or a deletedportion of data, erasure of the erasure immune files, blocks or portionsof data is prevented during garbage collection, in an action 710. Thatis, there are no other copies of the data for that data to be garbagecollected. The erasure immune files, blocks or portions of data are madeavailable for reference during deduplication of further user data, in anaction 712.

It should be appreciated that the methods described herein may beperformed with a digital processing system, such as a conventional,general-purpose computer system. Special purpose computers, which aredesigned or programmed to perform only one function may be used in thealternative. FIG. 8 is an illustration showing an exemplary computingdevice which may implement the embodiments described herein. Thecomputing device of FIG. 8 may be used to perform embodiments of thefunctionality for a storage node or a non-volatile solid state storagein accordance with some embodiments. The computing device includes acentral processing unit (CPU) 801, which is coupled through a bus 805 toa memory 803, and mass storage device 807. Mass storage device 807represents a persistent data storage device such as a disc drive, whichmay be local or remote in some embodiments. The mass storage device 807could implement a backup storage, in some embodiments. Memory 803 mayinclude read only memory, random access memory, etc. Applicationsresident on the computing device may be stored on or accessed via acomputer readable medium such as memory 803 or mass storage device 807in some embodiments. Applications may also be in the form of modulatedelectronic signals modulated accessed via a network modem or othernetwork interface of the computing device. It should be appreciated thatCPU 801 may be embodied in a general-purpose processor, a specialpurpose processor, or a specially programmed logic device in someembodiments.

Display 811 is in communication with CPU 801, memory 803, and massstorage device 807, through bus 805. Display 811 is configured todisplay any visualization tools or reports associated with the systemdescribed herein. Input/output device 809 is coupled to bus 805 in orderto communicate information in command selections to CPU 801. It shouldbe appreciated that data to and from external devices may becommunicated through the input/output device 809. CPU 801 can be definedto execute the functionality described herein to enable thefunctionality described with reference to FIGS. 1-7. The code embodyingthis functionality may be stored within memory 803 or mass storagedevice 807 for execution by a processor such as CPU 801 in someembodiments. The operating system on the computing device may beMS-WINDOWS™, UNIX™, LINUX™, iOS™, CentOS™, Android™, Redhat Linux™,z/OS™, or other known operating systems. It should be appreciated thatthe embodiments described herein may be integrated with virtualizedcomputing system also.

Detailed illustrative embodiments are disclosed herein. However,specific functional details disclosed herein are merely representativefor purposes of describing embodiments. Embodiments may, however, beembodied in many alternate forms and should not be construed as limitedto only the embodiments set forth herein.

It should be understood that although the terms first, second, etc. maybe used herein to describe various steps or calculations, these steps orcalculations should not be limited by these terms. These terms are onlyused to distinguish one step or calculation from another. For example, afirst calculation could be termed a second calculation, and, similarly,a second step could be termed a first step, without departing from thescope of this disclosure. As used herein, the term “and/or” and the “/”symbol includes any and all combinations of one or more of theassociated listed items.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising”, “includes”, and/or “including”, when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. Therefore, the terminology usedherein is for the purpose of describing particular embodiments only andis not intended to be limiting.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

With the above embodiments in mind, it should be understood that theembodiments might employ various computer-implemented operationsinvolving data stored in computer systems. These operations are thoserequiring physical manipulation of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated. Further, the manipulationsperformed are often referred to in terms, such as producing,identifying, determining, or comparing. Any of the operations describedherein that form part of the embodiments are useful machine operations.The embodiments also relate to a device or an apparatus for performingthese operations. The apparatus can be specially constructed for therequired purpose, or the apparatus can be a general-purpose computerselectively activated or configured by a computer program stored in thecomputer. In particular, various general-purpose machines can be usedwith computer programs written in accordance with the teachings herein,or it may be more convenient to construct a more specialized apparatusto perform the required operations.

A module, an application, a layer, an agent or other method-operableentity could be implemented as hardware, firmware, or a processorexecuting software, or combinations thereof. It should be appreciatedthat, where a software-based embodiment is disclosed herein, thesoftware can be embodied in a physical machine such as a controller. Forexample, a controller could include a first module and a second module.A controller could be configured to perform various actions, e.g., of amethod, an application, a layer or an agent.

The embodiments can also be embodied as computer readable code on anon-transitory computer readable medium. The computer readable medium isany data storage device that can store data, which can be thereafterread by a computer system. Examples of the computer readable mediuminclude hard drives, network attached storage (NAS), storage areanetwork, read-only memory, random-access memory, CD-ROMs, CD-Rs, CD-RWs,magnetic tapes, and other optical and non-optical data storage devices.The computer readable medium can also be distributed over a networkcoupled computer system so that the computer readable code is stored andexecuted in a distributed fashion. Embodiments described herein may bepracticed with various computer system configurations includinghand-held devices, tablets, microprocessor systems, microprocessor-basedor programmable consumer electronics, minicomputers, mainframe computersand the like. The embodiments can also be practiced in distributedcomputing environments where tasks are performed by remote processingdevices that are linked through a wire-based or wireless network.

Although the method operations were described in a specific order, itshould be understood that other operations may be performed in betweendescribed operations, described operations may be adjusted so that theyoccur at slightly different times or the described operations may bedistributed in a system which allows the occurrence of the processingoperations at various intervals associated with the processing.

In various embodiments, one or more portions of the methods andmechanisms described herein may form part of a cloud-computingenvironment. In such embodiments, resources may be provided over theInternet as services according to one or more various models. Suchmodels may include Infrastructure as a Service (IaaS), Platform as aService (PaaS), and Software as a Service (SaaS). In IaaS, computerinfrastructure is delivered as a service. In such a case, the computingequipment is generally owned and operated by the service provider. Inthe PaaS model, software tools and underlying equipment used bydevelopers to develop software solutions may be provided as a serviceand hosted by the service provider. SaaS typically includes a serviceprovider licensing software as a service on demand. The service providermay host the software, or may deploy the software to a customer for agiven period of time. Numerous combinations of the above models arepossible and are contemplated.

Various units, circuits, or other components may be described or claimedas “configured to” perform a task or tasks. In such contexts, the phrase“configured to” is used to connote structure by indicating that theunits/circuits/components include structure (e.g., circuitry) thatperforms the task or tasks during operation. As such, theunit/circuit/component can be said to be configured to perform the taskeven when the specified unit/circuit/component is not currentlyoperational (e.g., is not on). The units/circuits/components used withthe “configured to” language include hardware—for example, circuits,memory storing program instructions executable to implement theoperation, etc. Reciting that a unit/circuit/component is “configuredto” perform one or more tasks is expressly intended not to invoke 35U.S.C. 112, sixth paragraph, for that unit/circuit/component.Additionally, “configured to” can include generic structure (e.g.,generic circuitry) that is manipulated by software and/or firmware(e.g., an FPGA or a general-purpose processor executing software) tooperate in manner that is capable of performing the task(s) at issue.“Configured to” may also include adapting a manufacturing process (e.g.,a semiconductor fabrication facility) to fabricate devices (e.g.,integrated circuits) that are adapted to implement or perform one ormore tasks.

The foregoing description, for the purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the embodiments and its practical applications, to therebyenable others skilled in the art to best utilize the embodiments andvarious modifications as may be suited to the particular usecontemplated. Accordingly, the present embodiments are to be consideredas illustrative and not restrictive, and the invention is not to belimited to the details given herein, but may be modified within thescope and equivalents of the appended claims.

What is claimed is:
 1. A method for extending reference data lifetime indeduplication, comprising: determining that a quantity of user data hasat least a threshold amount of data that is re-created in a storagesystem; and protecting at least portions of the quantity of user datafrom erasure by garbage collection in the storage system during apredetermined time interval, wherein the protected at least portions areavailable for deduplication of further user data in the storage systemduring the predetermined time interval.
 2. The method of claim 1,wherein the determining comprises: forming a data structure, over one ormore sampling windows of time, of data of the storage system, the datastructure indicating amounts of the data of files or blocks in thestorage system having hash function results matching hash functionresults of at least one other file or block seen during the one or moresampling windows of time.
 3. The method of claim 1, wherein theprotecting is based on metadata that includes an aging parameter foreach of the at least portions of the quantity of user data, and furthercomprising: setting the aging parameter for one of the at least portionsof the quantity of user data to a first value, responsive to determiningthe one of the at least portions matches a fingerprint result of a fileor block seen during a sampling window of time, wherein the first valueindicates to not erase during garbage collection; and adjusting theaging parameter for a further one of the at least portions of thequantity of user data to a second value, responsive to determining thefurther one of the at least portions has a fingerprint result unmatchedby files or blocks seen during the sampling window of time, wherein thesecond value indicates to erase during garbage collection.
 4. The methodof claim 1, further comprising: performing garbage collection, whichincludes erasing portions of storage memory of the storage system,corresponding to files that the storage system considers no longer inexistence, except where metadata prevents the erasure during the garbagecollection.
 5. The method of claim 1, further comprising: performinggarbage collection, which includes erasing a plurality of fingerprintsnot matched in at least one deduplication operation, except where afingerprint, corresponding to one of the at least portions of thequantity of user data is protected from erasure.
 6. The method of claim1, wherein the determining is on a basis of a file, a file type, a blockor a range of blocks, and wherein the threshold amount of data is one ormore times as much as a data chunk corresponding to a fingerprint or ahash function result.
 7. The method of claim 1, further comprising:establishing in metadata that at least portions of the quantity of userdata are to have erasure immunity in the storage system for thepredetermined time interval; and writing to a table in the storagesystem, regarding how often incoming data to the storage systemre-creates a same data or includes greater than the threshold amount ofdata that is re-created.
 8. A deduplication method comprising:identifying user data having at least a threshold amount of data that isre-created, by one or more applications; writing an indicator tometadata associated with the identified user data, wherein the indicatorestablishes a time interval of erasure immunity; and preventing at leastportions of the user data from being erased during garbage collection,during the time interval in accordance with the indicator, wherein theat least portions of the identified user data are kept available duringthe time interval of erasure immunity as reference data fordeduplication of further data.
 9. The method of claim 8, furthercomprising: generating a histogram tracking re-creation of files orblocks over one or more sampling windows of time; and adjusting a valueof the threshold amount based on the histogram.
 10. The method of claim8, further comprising: setting an aging parameter of the indicator inmetadata at a start of the time interval; and adjusting the agingparameter towards allowance of erasure, responsive to one of completinga cycle of garbage collection or a passage of time.
 11. The method ofclaim 8, further comprising: tracking one of file creation, filedeletion, block creation, block deletion, object creation, objectdeletion or frequency of re-creation of data, in a metadata table; andadjusting the time interval based on the tracking.
 12. The method ofclaim 8, further comprising: adjusting a value of the threshold amount,based on utilization of storage capacity of the storage system.
 13. Themethod of claim 8, further comprising: performing garbage collection, toerase portions of storage memory of the storage system except where theindicator establishes the time interval of erasure immunity for the atleast portions of the identified user data.
 14. A storage system,comprising: storage memory; and at least one processor of the storagesystem, configured to write an indicator to metadata of the storagesystem, the indicator protecting at least portions of user data fromerasure during garbage collection, for a time interval, responsive tothe at least one processor identifying the user data as having at leasta threshold amount of data that is re-created on a periodic basis,wherein the at least portions of the user data associated with theindicator are available during the time interval as a reference fordeduplication.
 15. The storage system of claim 14, further comprising:the at least one processor configured to generate a data structure ofuser data over time, the data structure indicating at least one of:frequency of re-creation of data or amount of re-created data, whereinthe identifying is based on the data structure.
 16. The storage systemof claim 14, further comprising: the at least one processor configuredto monitor amount of storage capacity of the storage memory utilized andto adjust the time interval or a value of the threshold amount based onthe amount of storage capacity utilized.
 17. The storage system of claim14, further comprising: the indicator including an aging parameter; theat least one processor configured to adjust the aging parameter towardsa first value, responsive to the identifying, wherein the first valueprevents the erasure during garbage collection; and the at least oneprocessor configured to adjust the aging parameter towards a secondvalue, responsive to one of passage of time or completion of a garbagecollection cycle, wherein the second value allows the erasure duringgarbage collection.
 18. The storage system of claim 14, furthercomprising: the at least one processor configured to perform in-linededuplication on data arriving for storage in the storage memory, withreference to the at least portions of the user data associated with theindicator.
 19. The storage system of claim 14, further comprising: theat least one processor configured to perform post-process deduplicationon data stored in the storage memory, with reference to the at leastportions of the user data associated with the indicator.
 20. The storagesystem of claim 14, further comprising: the at least one processorconfigured to perform a hash function on data arriving for storage inthe storage memory or data stored in the storage memory, wherein theidentifying is based on results of the hash function.